EFFECT OF SR-49059, A VASOPRESSIN V-1A ANTAGONIST, ON HUMAN VASCULAR SMOOTH-MUSCLE CELLS

The effects of SR-49059, a new nonpeptide and selective arginine vasop ressin (AVP) V-1a antagonist, were investigated in binding and functio nal studies on cultured human aortic vascular smooth muscle cells (VSM C). Characterization of human vascular V-1a receptors, using a specifi c V-1a radioiodinated ligand, showed that [I-125]-linear AVP antagonis t binding to human VSMC membranes was time dependent, reversible, and saturable. A single population of high-affinity binding sites (apparen t equilibrium dissociation constant = 15 +/- 6 pM; maximum binding den sity = 36 +/- 5 fmol/mg protein, i.e., similar to 3,000 sites/cell) wi th the expected V-1a profile was identified. Exposure of these cells t o AVP dose-dependently produced cytosolic free [Ca2+] increase [AVP co ncentration required to obtain a half-maximal response (EC(50)) = 23 /- 9 nM] and proliferation (EC(50) = 3.2 +/- 0.5 nM). SR-49059 strongl y and stereospecifically inhibited [I-125]-linear AVP antagonist bindi ng to VSMC V-1a receptors [inhibition constant (K-i) = 1.4 +/- 0.3 nM] , AVP-evoked Ca2+ increase [concentration of inhibitor required to obt ain 50% inhibition of specific binding (IC50) = 0.41 +/- 0.06 nM], and the mitogenic effects induced by 100 nM AVP (IC50 = 0.83 +/- 0.04 nM) . OPC-21268, another nonpeptide V-1a, antagonist, was more than two or ders of magnitude less potent than SR-49059 in these models. However, the consistent affinity (K-i = 138 +/- 21 nM) and activity found with OPC-21268 on human VSMC in comparison with the inactivity already obse rved for other human V-1a receptors (liver, platelets, adrenals, and u terus) strongly suggested the existence of human AVP V-1a-receptor sub types. In conclusion, SR-49059 displays high affinity for human vascul ar V-1a receptors and high potency in inhibiting the AVP physiological response on this tissue.